By decreasing the size of a pneumatic disc brake device (caliper brake device) used on a railway rolling stock, it is possible to reduce the overall aerodynamic resistance of a railway rolling stock by decreasing the weight and installation space of the brake device. For this reason, there is a great need for reductions in the size of a brake device particularly for high speed railway rolling stocks.
As shown in FIG. 9 of Patent Document 1 (JP 2008-296756 A) (that figure being attached hereto as FIG. 3), a conventional pneumatic disc brake device for a railway rolling stock has a pair of brake levers 22 and a pair of brake pads 24 disposed on both sides of a brake disc 25. Each of the brake pads is mounted on a brake head 23 which is pivotably mounted on one end of a brake lever 22 such that the pad opposes the brake disc 25. A pneumatic brake cylinder 21 is disposed between the other ends of the brake levers 22. In the figure, 26 indicates a link member which connects the pair of brake levers to each other, 22a indicates the fulcrum (pivoting point) of each brake lever, 22b indicates the center of support of the brake heads, and 25a indicates the frictional surfaces of the brake disc.
At the time of brake operation, compressed air is supplied to the brake cylinder from an unillustrated compressor to extend the brake cylinder 21. As a result, a force in the opposite direction, namely a contracting force acts on the other ends of the brake levers 22 on which the brake pads 24 are mounted, through the brake levers 22 having their fulcrums 22a which are fixed in space, and the brake pads 24 are pressed against the frictional surfaces 25a of the brake disc 25, thereby generating frictional resistance between the pads and the brake disc 25 and obtaining a braking force.
With such a pneumatic disc brake device, if the maximum pressure of compressed air which can be supplied to the brake cylinder is increased, a large pressing force can be produced using a brake cylinder with a small effective diameter, and a decrease in the size of the brake cylinder and accordingly of the disc brake device can be realized.
However, the maximum pressure of compressed air which can be supplied to the brake cylinder is determined by the capacity of the compressor mounted on the railway rolling stock, and usually it is limited to at most 1 MPa. Accordingly, there is a limit to the extent to which the size of the brake device can be decreased by increasing compressed air pressure.
Patent Document 2 (U.S. Pat. No. 5,813,499) proposes a disc brake device which has the object of achieving a decrease in size by decreasing the effective diameter of a brake cylinder. However, the disc brake device proposed in Patent Document 2 uses a complicated special link mechanism so as to generate a large braking force by the lever principle. Therefore, it had the problems of an increase in cost due to an increase in the number of parts and an increase in maintenance costs.